Sunday, April 14, 2024

Air Conditioner Reference Design

This reference design provides a comprehensive solution for air conditioner designs, such as window A/Cs and split A/Cs’ outdoor unit, offering a path to efficient and cost-effective A/C systems.

Modern A/C designs utilise an inverter-based variable speed drive for the brushless motor-based compressor and condenser fans to meet stringent energy efficiency ratings and power factor specifications. This approach allows optimal power settings, reducing overall power consumption compared to traditional fixed-speed single-phase AC induction motor (ACIM) drives. Power factor correction (PFC) is also essential for high-power appliances to ensure grid compatibility.

Microchip’s reference design utilises the dual-core dsPIC33CH family of digital signal controllers (DSCs) to efficiently control the condenser fan, compressor, PFC, and overall application logic. The high-performance dsPIC33C DSCs, including both Dual-core dsPIC33CH and Single-core dsPIC33CK models, provide ideal peripherals for dual motor control, allowing the replacement of three controllers with one for cost advantages. The design features a 220V, 1.8 KW power factor correction (PFC) stage with Digital Interleaved Boost technology, achieving an efficiency greater than 90%, a power factor of 0.991, and a total harmonic distortion (THD) of less than 5%. 

The condenser fan and compressor are powered by 120 W and 1.34 KW stages, respectively. The motor control aspect of the design supports both permanent magnet synchronous motors (PMSM) and interior permanent magnet synchronous motors (IPMSM). It includes an inverter stage capable of handling up to 1.4 KW and operates at a switching frequency range of 4 to 20 kHz. Variable speed control is achieved through sensorless field-oriented control (FOC), complemented by features such as torque compensation, field weakening, a PLL estimator, maximum torque per ampere (MTPA) for IPMSM, and stall detection.

To further enhance the functionality of the air conditioning system, the design includes temperature sensor interfaces for monitoring ambient air, inlet air, outlet air, and condenser temperature. It also provides control interfaces for solenoid valves and electronic expansion valves (stepper motor). A fly-back DC-DC converter generates the required 15-V, 12-V, and 3.3-V power rails. Optional support is available for using an AC induction motor (ACIM) or a built-in drive brushless DC motor (BLDC) for the condenser fan. Field communication support with the indoor unit is also included. The design addresses several design challenges, including reducing development time through a complete manufacturable solution, lowering the bill of materials (BOM) cost through a highly integrated design, and ensuring optimal performance with a high-efficiency FOC algorithm and reliable compressor start-up software. 

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Microchip has tested this reference design. It comes with a Bill of Material (BOM), schematics, etc. You can find additional data about the reference design on the company’s website. To read more about this reference design, click here.

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